drm/bridge: anx7625: fix an error code in anx7625_register_audio()

This code accidentally returns IS_ERR(), which is 1, instead of
propagating the negative error code.  The caller doesn't check for
errors so it doesn't affect run time at all.

Fixes: 566fef12 ("drm/bridge: anx7625: add HDMI audio function")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Tzung-Bi Shih <tzungbi@google.com>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20211124145219.GD13656@kili